Hydrolysates Derived From Decapterus Maruadsi Protein With Controlled Enzymatic Modification And Its Antioxidant Effect

About 7% of the sea fishing catch is decapterus maruadsi, which is not suitable for human, and usually used as feedstuffs. Thus the utilization of this natural resource is low. Decapterus maruadsi protein was used as resource in this paper, the hydrolysis parameters were optimized, the antioxidant abilities were assessed, the hydrolysates were purified by ion exchange chromatography, and then the antioxidant stability of hydrolysates under different processing and storage modes were discussed, which could be a theoretical support for the deeply processing of decapterus maruadsi.The composition of decapterus maruadsi shows it has high content of protein (22.60%), low content of fat (0.96%) and reasonable amino acid composition, which makes it a good substrate for hydrolysis. When compared to flavourzyme, protamex, trypsin and papain, it was proved that Alcalase produced antioxidant peptides most efficiently because the resulting hydrolysate showed the highest activity. Then the influences of hydrolysis time, temperature, and water-material ratio for enzymatic hydrolysis by Alcalase on decapterus maruadsi protein were inspected. And the results showed that the optimum hydrolytic conditions for reducing power was 50℃(temperature), 200min(time), 2.6(water-material ratio), which produced enzymatic hsydrolysate A (protein concentration was 10mg/ml) and the reducing power was 0.640; and for scavenging activity on hydroxyl free radical was 50℃(temperature), 220min(time), 2.2 (water -material ratio), which produced enzymatic hsydrolysate B(protein concentration was 10mg/ml), and the scavenging activity on hydroxyl free radical was 53.58%.The hydrolysates A and B were evaluated in different systems. In chemical system, it was found that the DPPH? scavenging rates of A and B (protein concentration was 5 mg/ml, the same below) were 84.86% and 86.30% respectively, which increased with the protein concentration, but the scavenging rate of A was lower than that of B; the ?OH scavenging rates of A and B were 36.81% and 38.67% respectively, and the corresponding EC50 were 11.25 mg/ml and 8.94 mg/ml; the reducing abilities of A and B were 0.383 and 0.339 respectively and the ferrous ions sequestration capacities were 4.65% and 14.93% respectively, which means the reducing ability of A was stronger than that of B, but the ferrous ions sequestration capacity of A was weaker than that of B. In yolk phospholipids oxidation system, the oxidant inhibition rates of A and B (protein concentration was 2 mg/ml) were 24.13% and 26.92%. In food system about Chinese Cantonese sausage, both of them could inhibit the acid value and peroxide value, and hydrolysate B was stronger than that of A. So as a whole Hydrolysate B was more effective in most systems in a comprehensively point.Hydrolysate B was purified by ion exchange chromatography. The static adsorption condition of anion ion resin: the capability of wet resin was 12.34mg/ml, the exchanged time was 2h, peptide was cleared by PB(0.05 mol/L), 0.3 mo1/L NaCl +0.06 mo1/L HAc, and the elution time were 1.5h and 2h. The static adsorption condition of cationic ion resin: the capability of wet resin was 20.2mg/ml, the exchanged time was 3h, peptide was cleared by ammonium acetate buffer (0.05 mo1/L), ammonia water (0.2 mo1/L), and the elution time were 1.5h and 2h. Three categories peptides (basic peptide, acidic peptide, neutral peptide) were separated from hydrolysate, the ?OH scavenging rates of them were 50.58%, 33.86% and 22.47% respectively, so the antioxidant activity of basic peptide was strongest. The antioxidant activity of basic peptide may be relevant to the amino acids including histidine, leucine and lysine, which were abundant in it through the amino acid analysis.The antioxidant stability of hydrolysate B was evaluated in different conditions such as temperature, pH, food materials, metal ions, dry processes, sterile processes and storage conditions. It was suggested that the hydrolysate B was heat-stable, it could keep highly antioxidant ability(90%) in the acidity environment, but lost its activity in the alkali environment, only 10% when pH was 9; Glucose and sodium benzoate would lower the antioxidant activity of the hydrolysate; all of K⁺,Ca²⁺,Mg²⁺,Zn²⁺,Cu²⁺ affected the antioxidant activity of hydrolysate, the keeping rates of antioxidant ability were 87.13%,88.66%,79.24% respectively, and even completely lost as Zn²⁺ and Cu²⁺ when the concentration was 100mg/L; the keeping rate was 93.50% by spray-drying, and it was 97.70% by freeze-drying. The influence of pasteurizer sterile process on antioxidant ability is less than that of boiling water, and the influence of autoclaves sterile process is the greatest. The hydrolysate B kept antioxidant ability (72.74%) in simulated digesting condition.